The World Wide Web consists of millions of specially formatted documents (called web pages) residing on servers connected to the Internet.

The Internet is a vast worldwide computer network. It consists of the hardware that connects computers together and allows them to communicate with each other. Contrary to popular belief, the Internet is not the same thing as the Web! (Web pages are only one of several services available over the Internet, as we will discuss a little later.)

Server software is software that runs on a server computer and provides the desired service. There is web server software for distributing web pages, email server software for delivering email, file transfer software for transferring files, etc.

Server hardware can run more than one type of server software at the same time. So, for example, a server computer can be both a web server and an email server, because both types of server software are running on it. (Note: sometimes the word "server" refers to the hardware, and sometimes it refers to the software, so it can be confusing. If you see a reference to a "web server" you can assume that it means a hardware server that is running web server software on it.)

Web pages are viewed by a special type of software on your computer called a web browser. (Netscape and Internet Explorer are the two most popular web browsers.) Web pages are written in HTML (HyperText Markup Language), and they contain only text. (If you open a web page with a text editor rather than a browser, all you will see is text-based HTML code.) However, HTML can include references to graphic, sound, animation, and video files. A browser has the ability to get a web page from a web server somewhere, interpret the HTML code, fetch the referenced files, and then construct the page on your computer monitor to look as the designer intended. Be aware, however, that each browser can interpret the HTML code a little differently, so the same page displayed by different browsers may not look exactly the same.

Every web page has a unique address, called a URL (Uniform Resource Locator). A URL specifies the server on which the web page resides, as well as the path on that server to find the specific web page. An example of a URL is:

iit.bloomu.edu/vthc/welcome.htm

• The above URL says that the web page is stored on the server named iit.bloomu.edu. (Web server names do not have to begin with "www", although most do. The only thing a computer needs to be a web server is to be running web server software.) Every server has a unique name, called a domain name. The Internet translates the domain name to a unique identifying number, called an IP address. With the IP address, your computer can talk to the remote server. (You can think of IP addresses as phone numbers that computers use to talk to each other!)
  
  
• The URL also says that the web page's name is welcome.htm, and that it can be found inside the vthc folder on the iit.bloomu.edu server. (Web pages usually have .htm or .html as an extension.)

Every browser has a place where you can type the URL of the web site you want to see. A web page can also contain links to other web pages, which take you to the specified web page when clicked upon (without typing anything). Either way, once the browser is given the URL, it knows which server the web page resides on and where it is stored on that server. With both of these pieces of information, the browser can:

1) talk to the appropriate server

2) ask the web server software on the server machine to locate and send the web page to the browser

3) receive the web page file from the server

4) interpret the HTML contents

5) request and receive any graphic, sound or video files referenced by the web page

6) construct the web page, incorporating any referenced files

7) display the web page

The web is an example of what is called client/server technology. The software on the client machine talks to the software on the server machine and they exchange information. In this case, the client software is your web browser, and the server software is the web server software running on the server machine.

Every client and server software pairing communicates using a specific protocol, or language. For example, web browsers communicate with web servers using the HTTP protocol.

The HTTP web protocol is just one of several protocols that computers use to communicate over the Internet. You can think of the Internet as a collection of telephones and the wires used to connect the phones together. When you use a telephone, you have to speak in a language that both sides understand. Languages are the equivalent of the various Internet protocols. Web browsers and servers talk to each other in Web language (HTTP); email clients and servers can talk to each other using the Post Office Protcol (POP); file transfers take place between servers and clients using the File Transfer Protocol (FTP); and other clients and servers use other languages or protocols as well.

Earlier we said that a URL looks something like this:

iit.bloomu.edu/vthc/welcome.htm

In actuality, complete URLs begin with "http://":

http://iit.bloomu.edu/vthc/welcome.htm

This tells the browser which protocol to use when communicating with the server. Of course, since HTTP is the standard protocol for the web, if you don't type the protocol the web browser simply assumes HTTP.

Below is a diagram showing different client and server computers talking to each other. Each service (the web, email, etc.) has its own protocol (http, pop, etc.) that the client and server software use to communicate.

As an example, look at the items in green: a file transfer client (Fetch) and a file transfer server (NcFTPd) are talking in the FTP language to carry out a file transfer.